It has been argued that the three most prominent cross-language syllable system patterns can be explained in terms of a few specific production and perception constraints (Redford, 1999), which are sufficient to explain the emergence if a week-organized, language-like syllable system from a randomly-organized system (Redford, Chen, Mikkulainen, 1998; 1999). Since the constraints on syllable patterns are universal, the question that arises from this research is how or why cross-language variation occurs. Two distinct possibilities are explored in the proposed research: (1) Variation occurs naturally as a result of the optimized process. If the production and perception constraints are fixed relative to one another, several good solutions (local minima) to the problem of constraint satisfaction may exist; (2) language communities may weight the same universal set of constrains differently because the constraints are flexible and often in conflict with one another. In this view, different languages represent different total solutions (global optima) to the problem of constrain satisfaction. Since we cannot exert direct control over language evolution, these possibilities are best examined via computational simulations. Thus a significant part of the work proposed is the development of a realistic, phonetically- and functionally-motivated model with which we will be able to stimulate the emergence of syllable systems. At first, genetic algorithms will be used to evolve vocabularies in which syllables and phonomes will co-evolve in response to functional constraints on the system. Later, a second level of evolution will be introduced to allow the model to match its output with actual language data and to adjust the weightings of the constraints associated with the output. The results of simulations conduct with these broad and theoretically-motivated model will help us understand how language variation occurs. The model will also give us insight into the evolution of the complex sound patterns of language and into the constraints that shape syllable systems. In future work, the model will be used to simulate the acquisition of speech in different language environments.